VLTI/MIDI Observations of the Massive Protostellar Candidate NGC 3603 IRS 9A

TL;DR

This study uses VLTI/MIDI mid-infrared interferometry to resolve the structure of the massive protostellar candidate IRS 9A, revealing a compact hot component and an asymmetric warm envelope, suggesting a circumstellar disk.

Contribution

First mid-infrared interferometric observations of IRS 9A revealing its complex structure and potential disk geometry, advancing understanding of massive protostar formation.

Findings

Resolved IRS 9A on all baselines with MIDI

Detected a steep visibility rise below 9 μm

Identified an asymmetric warm envelope and a compact hot component

Abstract

We used MIDI, the mid-infrared interferometric instrument of the VLTI, to observe the massive protostellar candidate IRS 9A, located at a distance of about 7 kpc at the periphery of the NGC 3603 star cluster. Our ongoing analysis shows that MIDI almost fully resolves the object on all observed baselines, yet below 9 $\mu$m we detect a steep rise of the visibility. This feature is modelled as a combination of a compact hot component and a resolved warm envelope which lowers the correlated flux at longer wavelengths. The extended envelope can already be seen in both MIDI's acquisition images and in complementary data from aperture masking observations at the Gemini South telescope. Its shape is asymmetric, which could indicate a circumstellar disk inclined against the line of sight. The compact component is possibly related to the inner edge of this (accretion) disk. The uncorrelated mid-infrared spectrum appears featureless and could be caused by optically thick emission without a significant contribution from the disk atmosphere.